The present invention relates to method and apparatus for measuring, without contact, the torque being applied from a source through an object to a load. More particularly, the invention relates to a sensing apparatus and method for measuring surface velocities at two points on the object transmitting the torque with sufficient precision to determine the twist experienced by the object from the difference in the measured velocities and thus the torque being transmitted.
Non-conducting sensors are desirable in industrial applications where noise, vibration, dirt and physical abuse make employment of contact sensors undesirable.
U.S. Pat. No. 3,604,804 issued to Carl M. Penney and Henry Hurwitz, Jr. on Sept. 14, 1971, discloses a method of measuring surface tangential velocity of a diffusely reflecting surface by measuring the Doppler frequency resulting from motion of speckles in the diffusely reflected light. A laser beam is divided into two separated beams which are then directed together so that they impinge on the same point on the surface. Due to the differing angles of arrival of the two beams at the surface, motion of the surface parallel to a plane defined by the two beams produces different Doppler frequencies. The Doppler produced by each beam is related to the angle of incidence of the incoming beams and the wave length of the light. A detector, sensing the light at the point of impingement can produce a signal which contains the difference between the Doppler frequencies of the two beams.
If it could be done with enough precision, measurement of rotational velocity of a shaft would be interpretable in terms of torsional vibration of the shaft. An electrical fault occurring in the transmission system to which a generator is coupled, resulting from load shedding, short circuits and the like produces extremely high oscillatory torques in the generator rotor. The torque history of such rotors is useful in predicting their expected life and in analyzing the complex relationship that exists between the electrical generation facility and the power transmission portion of the utility system.